1. Field of the Invention
The present invention relates to a method for removing a silicic compound from the waste liquor of steel pickling so as to recover therefrom high purity iron oxide powder.
2. Description of the Prior Art
As is well known, the hydrochloric acid pickling process has been mainly employed recently in the steel industry. The waste liquor of the hydrochloric acid pickling process is a ferrous chloride solution which is decomposed thermally into iron oxide and hydrochloric acid. The recovered hydrochloric acid is then used in the pickling process, and the recovered iron oxide is mainly used as the raw material of ferrite products and pigments. The impurities contained in the iron oxide are required to be in a small amount for ferrite production, and, especially in the case of the production of soft ferrite, the content of the silicic compound must be as low as possible.
Since it is difficult to remove the silicic compound from the iron oxide powder itself, a removing treatment must be applied before the decomposition process.
A centrifugation method and a recrystallization method are generally known for removing a silicic compound from the waste liquor of steel pickling. However, they involve fundamental difficulties in operation techniques so they are uneconomical methods.
A filtration method using a filter fabric or biscuit plate is sometimes applied to remove the silicic compound from the waste liquor of steel pickling after coagulation of the silicic compound in the liquor by some coagulation agent. As is well known since in the filtration method the particles are separated from the liquor by means of a filter in order to obtain a filtrate essentially free of particles, a fine filter must be used. The filter used in the filtration method can be embodied as a filter bed, in which the dimension of the through holes of the filter is decreased in the flowing direction of the waste liquor. The filtration method is impractical as an industrial method because the filtering medium becomes clogged after a short time when extremely fine and voluminous particles of the silicic compound are separated.
The prior art includes Japanese Unexamined Patent Publication No. 58-151335.